Bile, Gallbladder and Stones

Question 1

What is the function of the gallbladder?

Answer 1

• Storage and concentration of Bile - due to active Na+ transport out
• Bile becomes more acidic as Na+ is exchanged for H+

Question 2

What are the 3 phases in the control of gallbladder contraction?

What is the role of CCK and Secretin? What is its release triggered by?

LOOK AT DIAGRAM!

Answer 2

• • Cephalic Phase - Taste, smell, presence of food in mouth → impulses via vagus nerve
  • Gastric phase - Distension of stomach → impulses via the vagus nerve
  • Intestinal phase - CCK and Secretin for gallbladder emptying
• • CCK - stimulates contraction of gallbladder and relaxation of Sphincter of Oddi = ↑secretion - triggered by FAs in duodenum
  • Secretin - stimulates duct cells to release substances into bile - triggered by acid in duodenum

Question 3

What are the components of Bile?

What occurs to bile along the biliary tree?

How are substances moved across the bile canicular membrane? What substances are moved across?

Answer 3

• • Hepatocytes - produce cholesterol, lecithin, bile acids, bile pigments
  • Bile duct Epithelium: bicarbonate-rich salt solution (secretion influenced by Secretin)
• It’s composition is modified - water can be added, it savages substances (e.g. glucose, AA, GSH), and IgA and bicarbonate are secreted in response to Secretin

- By Specific transporters, including:
o	Bile acids
o	Cholesterol
o	Xenobiotics and Conjugated Bilirubin
o      Phosphatidylcholine

Question 4

What are Primary Bile acids?

What are Secondary Bile acids?

What occurs during the production of primary bile acids in the liver?

LOOK AT DIAGRAM!

Answer 4

• Cholic (MOST ABUNDANT) and Chenodeoxycholic acid are made in the LIVER from Cholesterol
• Modified versions of primary acids made by intestinal bacteria in COLON - include Deoxycholic acid and Lithocholic acid
• Cholesterol conjugated with Glycine/Taurine - ↑secretability and ↓toxicity

Question 5

What are the main functions of bile acids?

Answer 5

• Elimination of excess Cholesterol as Bile acids - prevent stones
• Absorption of Fat-soluble vitamins
• Regulate their own transport and metabolism in the enterohepatic circulation
• Digestion of TG’s - fat emulsification, lipid and glucose metabolism

Question 6

What is the role of cholesterol in Gallstone formation?

What causes the high cholesterol levels?

What are the 2 types of gallstones?

What is the consequence of a gallstone blocking the bile ducts?

Answer 6

• Stones have a higher concentration of cholesterol, which cause greater phospholipid and bile salt concentrations
• Excess liver secretion, reabsorption of bile salt and water
• • Cholesterol stones - more common - due to obesity
  • Calcium Bilirubinate (Pigment) stones - due to ↑conjugated bilirubin
• Obstruction = ↓Bile secretion, Nutritional deficiency, Jaundice (↑Free Bilirubin)

Question 7

What are the factors that affect Gallstone formation?

Answer 7

• Bile stasis - stones stay in the gallbladder rather than moving into ducts
• Decreased amount of bile acids due to malabsorption
• Chronic infection - bacteria may help formation of pigment stones
• Over-saturation of bile with cholesterol

Question 8

How are gallstones diagnosed?

Answer 8

• • USS and CT of right upper quadrant
  • Cholescintigraphy with radioactive tracer - image gallbladder and ducts
  • ERCP - visualise biliary tree by injecting contrast medium